I am also wondering the same thing! Did you ever find out?
Going by logic, the dual sim should be more expensive since it would have more utility... expanded memory microSD / or the option of a 2nd sim card.. whereas the single sim, only has sim + microSD card..
But I can get it for 200 euros cheaper than the single sim variant.. what's the catch??
Turns out ALL variations are dual sim. The single sim models are not true descriptions of the devices. I have disabled the second sim on the S10 and have put a micro SD card in the second sim tray instead.
The price variations are region specific pricing tactics.
The only true thing you need to be wary of is model number, i.e. if you buy a foreign model because its cheaper, it MAY not be able to receive updates? I ended up buying a model specific to my country.
If you do buy a cheaper model outside of your region, be prepared to go around lack of updates via manual downloads - you may lose Samsung pay functionality but google pay works